Semiconductor die singulation methods

ABSTRACT

In one embodiment, a method of singulating semiconductor die from a semiconductor wafer includes forming a material on a surface of a semiconductor wafer and reducing a thickness of portions of the material. Preferably, the thickness of the material is reduced near where singulation openings are to be formed in the semiconductor wafer.

The present application is a divisional of prior U.S. application Ser.No. 13/486,675, filed on Jun. 1, 2012, which is which is acontinuation-in-part application of prior U.S. application Ser. No.12/749,370, filed on Mar. 29, 2010, now U.S. Pat. No. 7,985,661 which isa continuation of prior U.S. application Ser. No. 11/834,924, filed onAug. 7, 2007, now U.S. Pat. No. 7,781,310, all of which have at leastone common inventor, a common assignee, and are hereby incorporatedherein by reference and priority thereto for common subject matter ishereby claimed.

BACKGROUND

The present invention relates, in general, to electronics, and moreparticularly, to methods of forming semiconductors.

In the past, the semiconductor industry utilized various methods andequipment to singulate individual semiconductor die from a semiconductorwafer on which the die was manufactured. Typically, a technique calledscribing or dicing was used to either partially or fully cut through thewafer with a diamond cutting wheel along scribe grids that were formedon the wafer between the individual die. To allow for the alignment andthe width of the dicing wheel each scribe grid usually had a largewidth, generally about one hundred fifty (150) microns, which consumed alarge portion of the semiconductor wafer. Additionally, the timerequired to scribe all of the scribe grids on the entire semiconductorwafer could take over one hour. This time reduced the throughput andmanufacturing capacity of a manufacturing area.

Another method of singulating individual semiconductor die used lasersto cut through the wafers along the scribe grids. However, laserscribing was difficult to control and also resulted in non-uniformseparation. Laser scribing also required expensive laser equipment aswell as protective equipment for the operators.

Accordingly, it is desirable to have a method of singulating die from asemiconductor wafer that increases the number of semiconductor die onthe wafer, that provides more uniform singulation, that reduces the timeto perform the singulation, and that has a narrower scribe line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a reduced plan view of an embodiment of asemiconductor wafer in accordance with the present invention;

FIG. 2 illustrates a cross-sectional view of an embodiment of a portionof the semiconductor wafer of FIG. 1 at a stage in a process ofsingulating die from the wafer in accordance with the present invention;

FIG. 3 illustrates a subsequent state in the process of singulating thedie from the wafer of FIG. 1 in accordance with the present invention;

FIG. 4 illustrates another subsequent stage in the process ofsingulating the die from the wafer of FIG. 1 in accordance with thepresent invention;

FIG. 5 illustrates an enlarged cross-sectional portion of semiconductordice that are formed on the wafer of FIGS. 1-4 and that are alternateembodiments of the dice that are explained in the description of FIGS.1-4;

FIG. 6 illustrates a subsequent stage in the process of singulating thedie of FIG. 6 in accordance with the present invention;

FIG. 7 illustrates another subsequent stage in the process ofsingulating the die of FIG. 6 in accordance with the present invention;

FIG. 8 illustrates a cross-sectional view of another embodiment ofanother portion of the semiconductor wafer of FIG. 1 at a stage in analternate process of singulating die from the wafer in accordance withthe present invention;

FIG. 9-FIG. 11 illustrate the semiconductor wafer of FIG. 1 atsubsequent stages in the alternate process of singulating the die fromthe wafer of FIG. 1 in accordance with the present invention;

FIG. 12 illustrates an enlarged plan view of the backside of wafer 10 inaccordance with the present invention;

FIG. 13 illustrates an enlarged cross-sectional view of a portion of thesemiconductor wafer of FIG. 11 in accordance with the present invention;

FIG. 14 illustrates an enlarged plan view of a backside of an alternateembodiment of wafer 10 in accordance with the present invention;

FIG. 15 illustrates a side view of a portion of an example of anembodiment of a tool for use in reducing a thickness of a material inaccordance with the present invention;

FIG. 16 illustrates a cross-sectional view the tool of FIG. 15 inaccordance with the present invention;

FIG. 17 illustrates an isometric view of the tool of FIG. 15 inaccordance with the present invention;

FIG. 18 illustrates an enlarged isometric view of a portion of asemiconductor wafer according to an example embodiment of a method ofusing the tool of FIG. 14-FIG. 16 in accordance with the presentinvention;

FIG. 19 illustrates an enlarged isometric view of a die of the wafer ofFIG. 1 after singulation from the wafer in accordance with the presentinvention;

FIG. 20 illustrates in a very general manner an isometric view of acutting tool formed to have multiple cutting tips in accordance with thepresent invention; and

FIG. 21 illustrates in a very general manner an isometric view of aganged tool for use in reducing a thickness of a material in accordancewith the present invention.

For simplicity and clarity of the illustration, elements in the figuresare not necessarily to scale, and the same reference numbers indifferent figures denote the same elements. Additionally, descriptionsand details of well-known steps and elements are omitted for simplicityof the description. For clarity of the drawings, doped regions of devicestructures are illustrated as having generally straight line edges andprecise angular corners. However, those skilled in the art understandthat due to the diffusion and activation of dopants the edges of dopedregions generally may not be straight lines and the corners may not beprecise angles. The terms first, second, third and the like in theclaims or/and in the Detailed Description of the Drawings, as used in aportion of a name of an element are used for distinguishing betweensimilar elements and not necessarily for describing a sequence, eithertemporally, spatially, in ranking or in any other manner. It is to beunderstood that the terms so used are interchangeable under appropriatecircumstances and that the embodiments described herein are capable ofoperation in other sequences than described or illustrated herein. Theuse of the word approximately or substantially means that a value of anelement has a parameter that is expected to be close to a stated valueor position. However, as is well known in the art there are always minorvariances that prevent the values or positions from being exactly asstated. It is well established in the art that variances of up to atleast ten per cent (10%) (and up to twenty per cent (20%) forsemiconductor doping concentrations) are reasonable variances from theideal goal of exactly as described.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a reduced plan view graphically illustrating, in a generalmanner, an example of an embodiment of a semiconductor wafer 10 that hasa plurality of semiconductor die, such as die 12, 14, and 16, formed onsemiconductor wafer 10. Die 12, 14, and 16 are spaced apart from eachother on wafer 10 by spaces in which singulation lines are to be formed,such as singulation lines 13 and 15. As is well known in the art, all ofthe plurality of semiconductor die generally are separated from eachother on all sides by areas where singulation lines such as lines 13 and15 are to be formed.

FIG. 2 illustrates an enlarged cross-sectional portion of wafer 10 ofFIG. 1 taken along section line 2-2. For clarity of the drawings and ofthe description, this section line 2-2 is illustrated to cross-sectiononly die 12 and portions of dice 14 and 16. Die 12, 14, and 16 may beany type of semiconductor die including a vertical transistor, a lateraltransistor, or an integrated circuit that includes a variety of types ofsemiconductor devices. Semiconductor dice 12, 14, and 16 generallyinclude a semiconductor substrate 18 that may have doped regions formedwithin substrate 18 in order to form active and passive portions of thesemiconductor die. The cross-sectional portion illustrated in FIG. 2 istaken along a contact pad 24 of each of dice 12, 14, and 16. Contact pad24 generally is a metal that is formed on the semiconductor die in orderto provide electrical contact between the semiconductor die and elementsexternal to the semiconductor die. For example, contact pad 24 may beformed to receive a bonding wire that may subsequently be attached topad 24 or may be formed to receive a solder ball or other type ofinterconnect structure that may subsequently be attached to pad 24.Substrate 18 includes a bulk substrate 19 that has an epitaxial layer 20formed on a surface of bulk substrate 19. A portion of epitaxial layer20 may be doped to form a doped region 21 that is used for formingactive and passive portions of semiconductor die 12, 14, or 16. Layer 20and/or region 21 may be omitted in some embodiments or may be in otherregions of dice 12, 14, or 16. Typically, a dielectric 23 is formed on atop surface of substrate 18 in order to isolate pad 24 from otherportions of the individual semiconductor die and to isolate each pad 24from the adjacent semiconductor die. Dielectric 23 usually is a thinlayer of silicon dioxide that is formed on the surface of substrate 18.Contact pad 24 generally is a metal with a portion of contact pad 24electrically contacting substrate 18 and another portion formed on aportion of dielectric 23. After dice 12, 14, and 16 are formed includingthe metal contacts and any associated inter-layer dielectrics (notshown), a dielectric 26 is formed over all of the plurality ofsemiconductor die to function as a passivation layer for wafer 10 andfor each individual semiconductor die 12, 14, and 16. Dielectric 26usually is formed on the entire surface of wafer 10 such as by a blanketdielectric deposition. The thickness of dielectric 26 generally isgreater than the thickness of dielectric 23.

FIG. 3 illustrates the cross-sectional portion of wafer 10 in FIG. 2 ata subsequent stage in an example of an embodiment of the process ofsingulating dice 12, 14, and 16 from wafer 10. After the passivationlayer of dielectric 26 is formed, a mask 32, illustrated by dashedlines, may be applied to the surface of substrate 18 and patterned toform openings that expose portions of dielectric 26 overlying each pad24 and also overlying portions of wafer 10 where the singulation lines,such as singulation lines 13 and 15, are to be formed. Thereafter,dielectric 26 is etched through the openings in mask 32 to expose theunderlying surface of pads 24 and of substrate 18. The openings that areformed through dielectric 26 in the region where the singulation lines,such as lines 13 and 15, are to be formed function as singulationopenings 28 and 29. The openings that are formed through dielectric 26overlying pads 24 function as contact openings. The etching processpreferably is performed with a process that selectively etchesdielectrics faster than it etches metals. The etching process generallyetches dielectrics at least ten (10) times faster that it etches metals.The material used for substrate 18 preferably is silicon and thematerial used for dielectric 26 preferably is silicon dioxide or siliconnitride. The material of dielectric 26 may also be other dielectricmaterials that can be etched without etching the material of pads 24,such as polyimide. The metal of pads 24 functions as an etch stop thatprevents the etching from removing the exposed portions of pads 24. Inthe preferred embodiment, a fluorine based anisotropic reactive ion etchprocess is used.

After forming the openings through dielectric 26, mask 32 is removed andsubstrate 18 is thinned to remove material from the bottom surface ofsubstrate 18 and reduce the thickness of substrate 18. Generally,substrate 18 is thinned to a thickness that is no greater than about onehundred to two hundred (100 to 200) microns. Such thinning proceduresare well known to those skilled in the art. After wafer 10 is thinned,the backside of wafer 10 may be metalized with a metal layer 27. Thismetalization step may be omitted in some embodiments. Aftermetalization, wafer 10 usually is attached to a transport tape orcarrier tape 30 that facilitates supporting the plurality of die afterthe plurality of die are singulated. Such carrier tapes are well knownto those skilled in the art.

FIG. 4 illustrates wafer 10 at a subsequent stage in the example processof singulating semiconductor die 12, 14, and 16 from wafer 10. Substrate18 is etched through singulation openings 28 and 29 that were formed indielectric 26. The etching process extends singulation opening 28 and 29from the top surface of substrate 18 completely through substrate 18.The etching process usually is performed using a chemistry thatselectively etches silicon at a much higher rate than dielectrics ormetals. The etching process generally etches silicon at least fifty (50)and preferably one hundred (100) times faster than it etches dielectricsor metals. Typically, a deep reactive ion etcher system which uses acombination of isotropic and anisotropic etching conditions is used toetch openings 28 and 29 from the top surface of substrate 18 completelythrough the bottom surface of substrate 18. In the preferred embodiment,a process commonly referred to as the Bosch process is used toanisotropically etch singulation openings 28 and 29 through substrate18. In one example, wafer 10 is etched with the Bosch process in anAlcatel deep reactive ion etch system.

The width of singulation openings 28 and 29 is generally five to ten(5-10) microns. Such a width is sufficient to ensure that openings 28and 29 can be formed completely through substrate 18 and are narrowenough to form the openings in a short time interval. Typically,openings 28 and 29 can be formed through substrate 18 within a timeinterval of approximately fifteen to thirty (15 to 30) minutes. Sinceall of the singulation lines of wafer 10 are formed simultaneously, allof the singulation lines can be formed across wafer 10 within the sametime interval of approximately fifteen to thirty (15 to 30) minutes.Thereafter, wafer 10 is supported by carrier tape 30 as wafer 10 istaken to a pick-and-place equipment 35 that is utilized to remove eachindividual die from wafer 10. Typically, equipment 35 has a pedestal orother tool that pushes each singulated die, such as die 12, upward torelease it from carrier tape 30 and up to a vacuum pickup (not shown)that removes the singulated die. During the pick-and-place process, theportion of thin back metal layer 27 that underlies openings 28 and 29breaks away and is left behind on tape 30.

FIG. 5 illustrates an enlarged cross-sectional portion of semiconductordice 42, 44, and 46 that are formed on wafer 10 and that are alternateembodiments of dice 12, 14, and 16 that are explained in the descriptionof FIGS. 1-4. Dice 42, 44, and 46 are illustrated at a manufacturingstate after forming dielectric 23 on the top surface of substrate 18 andprior to forming pads 24 (FIG. 1). Dice 42, 44, and 46 are similar todice 12, 14, and 16 except that dice 42, 44, and 46 each have arespective isolation trench 50, 54, and 58 that surround the die andisolate them from an adjacent die. Trenches 50, 54, and 58 generally areformed near an outside edge of each die. Trenches 50, 54, and 58 areformed to extend from the top surface of substrate 18 a first distanceinto bulk substrate 19. Each trench 50, 54, and 58 generally is formedas an opening into substrate 19 that has a dielectric formed on thesidewall of the opening and generally is filled with a dielectric orother material such as silicon or polysilicon. For example, trench 50may include a silicon dioxide dielectric 51 on the sidewalls of thetrench opening and may be filled with polysilicon 52. Similarly,trenches 54 and 58 include respective silicon dioxide dielectrics 55 and59 on the sidewalls of the trench opening and may be filled withpolysilicon 56 and 60. Singulation line 43 is to be formed betweentrenches 50 and 54, and singulation line 45 is to be formed betweentrenches 50 and 58. Trenches 50 and 54 are formed adjacent tosingulation line 43, and trenches 50 and 58 are formed adjacent tosingulation line 45. Methods of forming trenches 50, 54, and 58 are wellknown to those skilled in the art. It should be noted that trenches 50and 54 are used as illustration only and could be any number of shapes,sizes, or combinations of isolation tubs or trenches.

FIG. 6 illustrates wafer 10 at a subsequent stage in the alternateprocess of singulating semiconductor dice 42, 44, and 46 from wafer 10.After trenches 50, 54, and 58 are formed, other portions of dice 42, 44,and 46 are formed including forming contact pads 24 and formingdielectric 26 covering dice 42, 44, and 46. Dielectric 26 generally alsocovers other portions of wafer 10 including the portion of substrate 18where singulation lines 43 and 45 are to be formed. Thereafter, mask 32is applied and patterned to expose underlying dielectric 26 wheresingulation lines and contact openings are to be formed. Dielectric 26is etched through the openings in mask 32 to expose the underlyingsurface of pads 24 and of substrate 18. The openings that are formedthrough dielectric 26 in the region where the singulation lines, such aslines 43 and 45, are to be formed function as singulation openings 47and 48. The etching process used to form openings 47 and 48 throughdielectrics 23 and 26 is substantially the same as the process used toform openings 28 and 29 (FIG. 3) in dielectric 23 and 26. Openings 47and 48 preferably are formed so that dielectrics 51, 55, and 59 on thesidewalls of respective trenches 50, 54, and 58 are not underlyingopenings 47 and 48 so that the dielectrics will not be affected insubsequent operations to form singulation lines 43 and 45.

After forming openings 47 and 48 through dielectric 26, mask 32 isremoved and substrate 18 is thinned and metalized with metal layer 27 asexplained hereinbefore in the description of FIG. 3. This metalizationstep may be omitted in some embodiments. After metalization, wafer 10 isusually attached to carrier tape 30.

FIG. 7 illustrates wafer 10 at a subsequent stage in the alternateprocess of singulating semiconductor die 42, 44, and 46 from wafer 10.Substrate 18 is etched through singulation openings 47 and 48 that wereformed in dielectric 26. The etching process extends singulation opening47 and 48 from the top surface of substrate 18 completely throughsubstrate 18. Openings 47 and 48 usually are at least 0.5 microns fromdielectrics 51, 55, and 59. The etching process usually is an isotropicetch that selectively etches silicon at a much higher rate thandielectrics or metals, generally at least fifty (50) and preferably atleast one hundred (100) times faster. Since the dielectric on thesidewalls of the trenches protects the silicon of substrate 18, anisotropic etch can be used. The isotropic etch has a much higher etchingthroughput than can be obtained with the use of the BOSCH process orwith limited use of the Bosch process. However, the isotropic etchingtypically undercuts portions of substrate 19 that are underlyingtrenches 50, 54, and 58. Typically, a down-stream etcher with a fluorinechemistry is used to etch openings 28 and 29 from the top surface ofsubstrate 18 completely through the bottom surface of substrate 18 andexpose a portion of layer 27 underlying openings 28 and 29. In oneexample, wafer 10 is etched in the Alcatel deep reactive ion etch systemusing full isotropic etching. In other embodiments, isotropic etchingmay be used for most of the etching and anisotropic etching may be usedfor another portion of the etching (the Bosch process). For example,isotropic etching may be used until openings 28 and 29 extend to a depththat is substantially the same depth as trenches 50, 54, and 58, andanisotropic etching may be used thereafter to prevent the undercuttingof trenches 50, 54, and 58.

The width of singulation openings 47 and 48 is generally about the sameas the width of openings 28 and 29. Dice 42, 44, and 46 may be removedfrom tape 30 similarly to the manner of removing dice 12, 14, and 16.

FIG. 8 illustrates an enlarged cross-sectional portion of an example ofan embodiment of wafer 10 taken along a cross-section line 8-8 that isillustrated in FIG. 1. A thickness 70 of substrate 18 and wafer 10 isillustrated by an arrow. FIG. 8 illustrates additional singulation lines11 that are similar to singulation lines 13 and 15. A second surface 17of substrate 18 and wafer 10 is illustrated opposite to the surface onwhich layer 20 is formed.

FIG. 9 illustrates wafer 10 at a stage of an embodiment of one examplemethod of singulating die from wafer 10. In some embodiments, thickness70 of wafer 10 may be reduced. Typically, wafer 10 is inverted in orderto facilitate reducing thickness 70. In some embodiments, a supportstructure 34 may be attached to wafer 10 along the top surface in orderto facilitate thinning wafer 10. In other embodiments, support structure34 may be omitted. Thickness 70 may be reduced by methods such asback-grinding, chemical etching, chemical-mechanical polishing (CMP), orother means.

A conductor 37 is applied to surface 17. Typically, conductor 37 is ametal such as metal 27. However, conductor 37 may be a thicker metalthan metal 27, or may be other materials such as conductive epoxy, orthermal heat sink material, or other materials that do not include thematerial of substrate 19.

FIG. 10 illustrates wafer 10 at another subsequent stage of the examplemethod. Portions of conductor 37 that underlie regions of wafer 10 wheresingulation lines are to be formed may have the thickness reducedthereby forming reduced thickness regions 72 of conductor 37. Regions 72usually are formed to underlie portions of wafer 10 where singulationlines are to be formed such as lines 11, 13, and 15. Regions 72 may alsobe disposed at other portions of the plurality of semiconductor dies.Support structure 34 may or may not be utilized during this operation.

FIG. 11 illustrates wafer 10 at another subsequent stage of the examplemethod. Wafer 10 is mounted on tape 30. Tape 30 usually is applied towafer 10 in order to support wafer 10 during subsequent die singulationoperations. Conductor 37 overlies tape 30. Conductor 37 typically isdisposed on tape 30, however, in some embodiments there may be anintervening material between tape 30 and conductor 37. A support frame31 may be attached to tape 30 to facilitate handling tape 30 and wafer10.

Singulation openings, such as singulation openings 28, 29 or 43, 48, areformed in wafer 10 along the singulation lines, such as singulationlines 11, 13, 15, by methods such as those explained hereinbefore in thedescription of FIGS. 1-7. The singulation openings may also be formed bymethods such as those explained in related U.S. patent application Ser.No. 12/689,098 of inventor Gordon Grivna having a common assigneeherewith and a title of SEMICONDUCTOR DIE SINGULATION METHOD which wasfiled on Jan. 18, 2010 and is incorporated herein by reference.Typically, the width of the singulation openings is greater than thewidth of the widest portion of region 72.

Subsequently, an individual die, such as die 12, may be singulated fromthe remainder of wafer 10. For example, a pick-and-place operation maybe utilized to remove die 12 such as illustrated and explained in thedescription of FIG. 4.

During the singulation operation, regions 72 facilitate separating theportion of conductor 37 that underlie a semiconductor die, such asportion 75 underlying die 12, from the remainder of conductor 37.Because the thickness of conductor 37 has been reduced in regions 72,conductor 37 easily separates along regions 72 thereby leaving portion75 attached to die 12. In embodiments where regions 72 do not align withthe singulation openings, such as regions 72 being formed to both sidesof the singulation openings, regions 72 still facilitate separating theportion of conductor 37 that underlie a semiconductor die, such asportion 75 underlying die 12, from the remainder of conductor 37.Because conductor 37 has regions 72, in some embodiments conductor 37may have a thickness that is greater than metal 27.

In the preferred embodiment, regions 72 extend to approximately ninetypercent (90%) of the way through conductor 37 in order to facilitateseparation along regions 72. In other embodiments, regions 72 may extendcompletely through conductor 37. In some embodiments, surface 17 ofwafer 10 may be exposed by regions 72. In still other embodiments,forming conductor 37 may cause the formation of a metal-silicon alloyalong the interface between conductor 37 and substrate 18 or betweenconductor 37 and substrate 18. For such an embodiment, regions 72typically would not extend through the metal-silicon alloy.

FIG. 12 illustrates an enlarged plan view of the backside of wafer 10after forming conductor 37 and regions 72. Typically, regions 72 areformed to underlie all the singulation lines. Thus, regions 72 maytraverse wafer 10 and one direction and other regions 73 that aresimilar regions 72 may traverse wafer 10 in other directions in order tounderlie all the singulation lines of wafer 10.

FIG. 13 illustrates an enlarged plan view of a portion of wafer 10 neardie 12, 14, and 16. Preferably, regions 72 underlie the singulationopenings such as openings 28 and 29. In some embodiments, all or aportion of regions 72 may be offset from an edge of the singulationopenings by an offset distance 77, identified in general by an arrow.For example, the backside alignment may result is such offset or it maybe desirable to reduce the area of portion 75. It is believed that insome embodiments distance 77 may be five percent (5%) of the width ofthe die and still provide the desired uniform singulation of thesemiconductor die including portion 75.

FIG. 14 illustrates an enlarged plan view of a portion of an example ofan embodiment of a wafer 130 having hexagonal shaped die. Wafer 130 issimilar to wafer 10 except that the die have a hexagonal shape. The viewof FIG. 14 shows the shape of the die such as die 132 and 133, and alsoillustrates a bottom view to explain where a conductor, such asconductor 37, would have to be thinned to form reduced thickness regionssuch as regions 72 in FIG. 13. Conductor 37 is not illustrated forclarity of the explanation. For such a die configuration, several setsof reduced thickness regions 72 typically would be used to assist insingulating the die of wafer 130. Examples of reduced thickness regionssimilar to regions 72 are illustrated in a general manner as reducedthickness regions 135-137, 139-141, and 142. The reduced thicknessregions, such as regions 72, 135-137, 139-141, and 142, may not all beformed to only underlie the regions where the singulation lines orsingulation openings are to be formed because it would be difficult toform regions 72 in the pattern of the non-parallelogram shaped die. Insuch die patterns, reduced thickness regions, such as regions 72,135-137, 139-141, and 142, may also be formed to cross the wafer inregions near where the singulation lines and singulation openings arenot to be formed. For example, regions 135-137 may be formed near oneside of a series of die such as region 137 formed near one side of die132 to be near a singulation opening for die 132. Region 137 may alsotraverse wafer 130 near one side of other die that are aligned with die132. Region 137 may also cross under the interior of other die, such asdie 133, that are not aligned with die 132. Region 136 may be offset totraverse near one side of die 133 to be near a singulation opening fordie 133 and this may cause region 136 to also traverse under theinterior of die 132, for example under active regions of die 132.Another group of reduced thickness regions, such as regions 139-141, maytraverse wafer 130 along another side of the die, for example regions140 and 141 may traverse near two opposite sides of die 132 to be nearother singulation openings for die 132. This may cause region 141 toalso traverse under the interior of die 133 because of the off-setrelationship of the die. Regions 142 may be formed to traverse acrosswafer 130 in another direction along another side of the die in order tobe near other singulation opening for the die. Thus in general, reducedthickness regions may be formed to traverse in groups in one directionand in other groups in another direction wherein portion of regions ofone group may be near an edge of a die such as underlying nearsingulation openings, while other regions of the group traverse tounderlie interior portions of other die. One skilled in the art willappreciate that such groups may also be formed for a wafer that has dieof different sizes, for example different sized parallelogram shapeddie. The reduced thickness regions may be formed in one group that arepositioned near an edge of die of one size to be near singulationopenings for that die and may underlie interior portions of other diewhich have a different size.

One skilled in the art will appreciate that such a method allows puttingthe hexagonal shaped die closer together and still being able touniformly singulate the die thereby increasing the number of die thatcan be formed in a given area of a wafer. Such a method also allowsputting die of different sizes closer together and increasing the numberof die that can be formed in a given area of a wafer.

FIG. 15 illustrates a side view of a portion of an example of anembodiment of a tool 80, such as a cutting tool or scribing tool, thatmay be used to form regions 72.

FIG. 16 illustrates a cross-sectional view of tool 80 taken all along across-sectional line 14-14.

FIG. 17 illustrates an isometric view of tool 80. This description hasreferences to FIGS. 13-15. Tool 80 includes a cutting tip 89 and acutting surface 88 that is adjacent to tip 89 and extends from tip 89toward a central support section 82 of tool 80. Tip 89 and cuttingsurfaces 88 are configured to engage with a material which is to bescribed or cut, such as conductor 37 on wafer 10, and reduce thethickness of the material, such as forming regions 72 in conductor 37.Tool 80 also includes a depth stop 83 that is configured to limit thepenetration of tip 89 and surfaces 88 into the material. Tip 89 isformed to extend a cutting distance 96 from stop 83. Distance 96 is thedistance that tip 89 and surface 88 may extend into or penetrate thematerial to be cut.

Typically, tip 89 and surface 88 are configured as a cutting wheel thatrolls along the material so that tip 89 and surfaces 88 penetrate intothe material as tool 80 rotates along the material. For such anembodiment, surface 88 is rotatingly attached to section 82. Althoughtip 89 is illustrated as a sharp or pointed tip, tip 89 may have variousconfigurations including a blunt tip as illustrated by a dashed line102. The portion of cutting surface 88 that extends distance from depthstop 83, illustrated by a dashed line 103, to tip 89 forms a cuttingvolume for tool 80.

Tool 80 typically includes a central opening 92 that extends along amajor axis 93. In most embodiments, a shaft is typically insertedthrough central opening 92 so that tool 80 may rotate around the shaft.

In the preferred embodiment, central support section 82 is a solid piecethat has a width which is greater than a width 98 of surface 88. Inother embodiments, section 82 may be formed from multiple elements thatare abutted together to form section 82. For example, section 82 mayseparate into pieces as illustrated by dashed lines 120 and 121. Thesepieces may be abutted together to form tool 80. For example, the shaftthrough opening 92 may hold the pieces together. Although tool 80 isillustrated with opening 82, in other embodiments opening 92 may beomitted. In other embodiments, tool 80 may have an attachment device,such as a peg or screw, extending from section 82 along axis 93 and theattachment device may be used to section 82 and other portions of tool80.

During the process of using tool 80 for scribing or cutting thematerial, the cutting volume of tool 80 usually causes portions of thematerial to be displaced or forced out from within the material uptoward the surface of the material. In order to control the portions ofthe material that are displaced and to assist in more accurate controlof the cutting depth, tool 80 includes an accumulation region 86(indicated in general by an arrow). Accumulation region 86 provides aspace for displaced material to accumulate as tool 80 is cutting orscribing the material. Accumulation region 86 minimizes the forced outmaterial from coming between depth stop 83 and the surface of thematerial being cut or scribed. Consequently, as the displaced materialis forced out it is accumulated by region 86 so that tip 89 may extenddistance 96 into the material. As will be explained further hereinafter,the displaced material accumulated within region 86 usually is extrudedtoward the surface of the material as tool 80 moves across the material.

Typically, accumulation region 86 is formed as a recess in section 82and adjacent to surface 88. Region 86 has sides 90 and 91 that extendinto section 82 away from surface 88 and away from stop 83. Preferably,recess 86 is formed to have a volume that is approximately the same asthe cutting volume so that the forced out material may substantially fitwithin accumulation region 86. In some embodiments, the volume of theaccumulation region may be less than the cutting volume, but such aconfiguration may cause excess material in regions 72. In otherembodiments the volume of region 86 may be greater than the cuttingvolume. In one embodiment, the volume of the accumulation region is noless than the cutting volume. In the preferred embodiment, surface 88extends at an angle 84 of approximately one hundred ten degrees (110)from a line parallel to the surface to be cut. For example, angle 84 maybe from surface 88 to the surface of stop 83. Angle 84 typically canvary from about ninety five to about one hundred thirty five (95-135)degrees and still provide the desired accurate depth control and canalso provide uniform separation of the material. For example, to provideuniform separation during the singulation of semiconductor die. Thoseskilled in the art will appreciate that the relationship between thecutting and accumulation volumes should be maintained as angle 84changes.

Although accumulation region 86 is illustrated as a triangle, sides 90and 91 may have various shapes that facilitate accumulating the extrudedmaterial. For example, tip 89 can have a width from 0.2 to 0.55 micronsfor respective distance 96 of one to three (1-3) microns.

FIG. 18 illustrates an enlarged isometric view of a portion of asemiconductor wafer 110 that is similar to wafer 10. Wafer 110 includesa substrate 111 that is similar to substrate 18. A conductor 113 isformed on a surface of wafer 110 similar to conductor 37. In anoperation, tool 80 was engaged with conductor 113 and moved across thesurface of conductor 113 to reduce the thickness of conductor 113. Tip89 and surfaces 88 penetrated into conductor 113 and stop 83 abutted thesurface of conductor 113. As tool 80 moved across conductor 113, areduced thickness region 115 was formed. In one embodiment, region 115could be considered as a trough formed in conductor 113. The penetrationof tool 80 displaced portions of conductor 113 out of conductor 113.These displaced or forced out portions were controlled within region 86of tool 80 and formed onto the surface of conductor 113 as ridges 116 onthe surface of conductor 113 adjacent to the region 115.

Without accumulation region 86, the displaced material may have beenleft behind within region 115 thereby causing an irregular depth withinregion 115, or may have stuck to the surface of the tool used to formregion 115 thereby also forming an irregular depth. The irregular depthcould result in non-uniform separation of the material during diesingulation. The irregular depth also could result in irregular debrisor contamination thereby resulting in unusable semiconductor die.

Those skilled in the art will appreciate that although the method ofsingulating die from wafer 10 is explained to form the reduced thicknessregions prior to forming the singulation openings, the sequence could bechanged. For example, wafer 10 could be applied to tape 30 and thesingulation openings formed, then the reduced thickness regions could beformed in conductor 37. For example, the reduced thickness regions maybe formed from either side of the singulation openings. Additionally,regions 72 may be formed by means other than with tool 80. For example,regions 72 may be formed by photoresist masking and etching, a waferscribe tool, a saw blade, or laser ablation. In some embodiments, tool80 may be used to make multiple passes across a material, material 113for example, in order to form regions 72 to the desired depth. Forexample tool 80 may make one pass to form regions 72 to a first depthand another pass to form regions 72 to a greater depth.

In some embodiments, a cutting tool may be formed to have multiplecutting tips 88 to enable simultaneous cutting of multiple regions 72 asillustrated by a multiple cutting tool 145 in FIG. 20. Two tools 80 maybe configured to simultaneously thin two regions 72 during one pass. Thetwo tools 80 may be arranged substantially parallel along axis 93. Inother embodiments, the tools may be parallel but not aligned along axis93. In other embodiments, the tool 80 may be formed to have differentdistances 96 and/or angles 102.

FIG. 19 illustrates an enlarged isometric view of die 12 aftersingulation from wafer 10 and after attachment to a mounting platform155. Platform 155 may be a portion of a semiconductor package, such as aflag region, or may be a portion of another type of platform suitablefor mounting die 12. Connections usually are made to electricallyconnect portions of die 12 to elements external to die 12. For example,a connection 164 may be formed between a connection pad 163 of die 12and electrical traces on platform 155.

In some cases, it may be desirable to electrically connect conductor 37or a portion of conductor 37 to electrical connection points on platform155 or to electrical connection points on die 12 (illustrated in generalby dashed lines). During the steps of forming singulation openings forsingulating die 12, the methods used for forming the singulationopenings may be used to form an opening in an interior of die 12 such asan opening 158. Opening 158 may be formed to expose a portion ofconductor 37. Subsequently, a connection 160 may be attached to theportion of conductor 37 that is exposed in opening 158.

In some cases, it may also be desirable to isolate the portion ofconductor 37 that is connected to connection 160 from other portions ofconductor 37. Regions 72 may be used to separate conductor 37 intoportions or sections. Regions 72 may be formed underlying interiorportions of die 12 to separate one portion of conductor 37, such as aportion 167 to which connection 160 is electrically attached, from otherportions of conductor 37.

Connection 160 is illustrated as a bonding wire connection; however,those skilled in the art will understand that other types of connectionmechanisms may be used to form the connections and provide an electricalconnection between the elements.

FIG. 21 schematically illustrates in a very general manner an isometricview of a ganged tool 150 that may be used to reduce the thickness of aregion of a material, for example a material on a surface of asemiconductor wafer. Tool 150 is similar to tool 80 but includes asupport section that is suitable for accommodating a plurality of tools80. Tool 150 may be used to make multiple passes along a region, such asa region 72, to reduce the thickness of the region. In some embodiments,one of the tool 80 elements may be set to have a first depth into thematerial to be reduced and another of the tool 80 elements may have asecond depth that is greater than the first depth. Those skilled in theart will appreciate that one of those two depths may or may not belimited by surface 83. In other embodiments, two or more of tool 80elements may have the same depth, or another one or more of the tool 80elements may have a different depth. In some embodiments, tools 80 oftool 150 may have different angles 102 from each other and/or may havedifferent shapes of surface 88 and/or tip 89 to facilitate cut profileand depth control. Tool 150 facilitates making multiple cuts into thematerial in one pass across the material thereby reducing cycle time andassociated manufacturing costs. Tool 150 can also reduce the pressurerequirements needed by a single tool 80 thereby further improving theuniformity of the cut.

Tool 150 includes vertical supports 151 that are formed to engage withand support a tool 80. A projection from support 151 could mate toopening 92 of tool 80 (see FIGS. 15-17) to support tool 80. Supports 151extend from another support 153 that is attached to a means for movingand controlling tool 150.

Those skilled in the art will appreciate that in one embodiment, Amethod of singulating semiconductor die from a semiconductor wafercomprises: providing a semiconductor wafer, a wafer 10 for example,formed from a silicon semiconductor material and having a plurality ofsemiconductor dies formed on a first surface of the semiconductor wafer,the plurality of semiconductor dies separated from each other bysingulation regions where singulation openings, such as openings 28 and29, are to be formed wherein the plurality of semiconductor dies includea dielectric layer overlying portions of the plurality of semiconductordies, the semiconductor wafer including a second surface that isopposite to the first surface; forming a conductor, conductor 37 forexample, on the second surface of the semiconductor wafer, the conductorhaving a thickness; reducing the thickness of portions of the conductorto form a reduced thickness region, such as a region 72, of theconductor; attaching the semiconductor wafer to a carrier tape, acarrier tape 30 for example, wherein the conductor overlies the carriertape; and etching a first opening, opening 28 for example, to extendinto the semiconductor wafer thereby creating a space between theplurality of semiconductor dies wherein the carrier tape remainsattached during the etching.

In another embodiment, the method may also include separating onesemiconductor die of the plurality of semiconductor dies from thecarrier tape and from other die of the plurality of semiconductor dieswherein a first portion of the conductor remains attached to the onesemiconductor die and is separated from other portions of the conductoralong the reduced thickness region.

In other embodiments, the method may further include etching the firstopening from the first surface of the semiconductor wafer through thesemiconductor wafer to the second surface.

Another embodiment may include that the step of reducing the thicknessof the portions of the conductor to form the reduced thickness regionsincludes forming the reduced thickness regions in the portions of theconductor that underlie the singulation regions.

Still other embodiments may include, wherein etching the first openingincludes using etching the first opening to expose a surface of thesemiconductor wafer; and etching through the first opening to extend adepth of the first opening into the semiconductor wafer thereby creatingthe space between the plurality of semiconductor dies wherein thecarrier tape remains attached during the etching.

Those skilled in the art will appreciate that in one embodiment, acutting tool, for example tool 80, comprises: a central support section,section 82 for example, having a major axis, such as an axis 93; acutting tip, for example tip 89; a cutting surface, surface 88 forexample, adjacent to the cutting tip and extending from the cutting tiptoward the central support section terminating in a distal end, distalend 103 for example, of the cutting surface wherein the cutting surfaceis attached to the central support section; a depth stop, stop 83 forexample, spaced a first distance from the cutting tip toward the centralsupport section wherein a first volume, such as a cutting volume, isformed by a portion of the cutting surface extending from the cuttingtip to the depth stop; and an accumulation region, region 86 forexample, adjacent to the central support section and extending away fromthe cutting surface, the accumulation region having a second volume,such as a volume 86, that approximates the first volume.

Another embodiment may include that the accumulation region extends fromthe distal end of the cutting surface away from the cutting tip.

Other embodiments mat include that the depth stop has a first portionthat is configured to engage with a surface of a conductor on asemiconductor wafer to limit a depth of penetration of the cutting tipinto the conductor.

In another embodiment, the accumulation region is a formed as a recess,such formed by sides 90 and 91, disposed within the central supportsection, the accumulation region positioned adjacent to the distal endof the cutting surface and extending from the distal end of the cuttingsurface into the central support section.

In still another embodiment, the central support section may berotatingly coupled to the cutting surface, for example the centralsupport section may be formed to rotate about an axis to cause thecutting surface to also rotate.

Those skilled in the art will also appreciate that a method of forming atool, tool 80 for example, for a semiconductor wafer comprises: formingthe tool to reduce a thickness of a material, material represented byconductor 37 for example, formed on a semiconductor wafer, such as wafer10; forming the tool with a cutting tip, such as tip 89, and cuttingsurfaces, such as surface 88, that are configured to penetrate into thematerial to form reduced thickness regions, region 72 for example, inthe material; and forming an accumulation region, region 86 for example,of the tool with a recess having a first volume for accepting portionsof the material displaced from within the material by the penetration.

Those skilled in the art will also understand that in one embodiment, amethod of singulating semiconductor die from a semiconductor wafercomprise: providing the semiconductor wafer, such as wafer 10, formedfrom a silicon semiconductor material and having a plurality ofsemiconductor dies, such as die 12 and 14, formed on a first surface ofthe semiconductor wafer and separated from each other by singulationregions of the semiconductor wafer where singulation openings, openings28 and 29 for example, are to be formed, the semiconductor waferincluding a second surface that is opposite to the first surface;providing a conductor on the second surface of the semiconductor wafer,the conductor having a thickness; engaging a cutting tool with theconductor to reduce the thickness of portions of the conductor, thecutting tool having a cutting tip and cutting surfaces that penetrateinto the conductor to form reduced thickness regions in the conductor;and moving the cutting tool across the conductor to form the reducedthickness regions.

In view of all of the above, it is evident that a novel device andmethod is disclosed. Included, among other features, is etchingsingulation openings completely through a semiconductor wafer. Etchingthe openings from one side assists in ensuring that the singulationopenings are substantially aligned to the semiconductor edge andpreferably are precisely aligned. Etching from one side also ensuresthat the singulation openings have very straight side-walls therebyproviding a uniform singulation line along each side of eachsemiconductor die. Etching the singulation openings completely throughthe semiconductor wafer facilitate forming narrow singulation linesthereby allowing room to use for forming semiconductor die on a givenwafer size. The etching process is faster than a sawing process, therebyincreasing the throughput of a manufacturing area.

While the subject matter of the invention is described with specificpreferred embodiments, it is evident that many alternatives andvariations will be apparent to those skilled in the semiconductor arts.For example, layers 20 and/or 21 may be omitted from substrate 18. Thesingulation openings alternately may be formed prior to or subsequent toforming the contact openings overlying pads 24. Also, the singulationopenings may be formed before thinning wafer 10, for example, thesingulation openings may be formed partially through substrate 18 andthe thinning process may be used to expose the bottom of the singulationopenings.

As the claims hereinafter reflect, inventive aspects may lie in lessthan all features of a single foregoing disclosed embodiment. Thus, thehereinafter expressed claims are hereby expressly incorporated into thisDetailed Description of the Drawings, with each claim standing on itsown as a separate embodiment of an invention. Furthermore, while someembodiments described herein include some but not other featuresincluded in other embodiments, combinations of features of differentembodiments are meant to be within the scope of the invention, and formdifferent embodiments, as would be understood by those skilled in theart.

The invention claimed is:
 1. A cutting tool comprising: a centralsupport section having a major axis; a cutting tip; a cutting surfaceadjacent to the cutting tip and extending from the cutting tip towardthe central support section terminating in a distal end of the cuttingsurface wherein the cutting surface is attached to the central supportsection; a depth stop spaced a first distance from the cutting tiptoward the central support section wherein a first volume is formed by aportion of the cutting surface extending from the cutting tip to thedepth stop; and an accumulation region adjacent to the central supportsection and extending away from the cutting surface, the accumulationregion having a second volume that approximates the first volume.
 2. Thecutting tool of claim 1 wherein the accumulation region extends from thedistal end of the cutting surface away from the cutting tip.
 3. Thecutting tool of claim 1 wherein the depth stop has a first portion thatis configured to engage with a surface of a conductor on a semiconductorwafer to limit a depth of penetration of the cutting tip into theconductor.
 4. The cutting tool of claim 1 wherein the central supportsection is rotatingly coupled to the cutting surface.
 5. The cuttingtool of claim 1 wherein the cutting surface angularly extends from thecutting tip to the central support section.
 6. The cutting tool of claim1 wherein the accumulation region is formed as a recess disposed withinthe central support section, the accumulation region positioned adjacentto the distal end of the cutting surface and extending from the distalend of the cutting surface into the central support section.
 7. Thecutting tool of claim 6 wherein the accumulation region has a widthextending laterally across the central support section.
 8. The cuttingtool of claim 6 wherein the depth stop is formed as a surface of thecentral support section that extends from a distal end of theaccumulation region away from the accumulation region.
 9. The cuttingtool of claim 1 wherein the depth stop is formed as a surface of aspacer attached to the central support section.